The advantages of current mode control in a DC-DC converter or DC-AC inverter are well known in the literature. It for most practical purposes reduces a second order system to a first order system making its control and current limiting easier to implement. Peak current or valley mode control are two typical methods of achieving this. These methods either detect only the peak or trough of the inductor current and make assumptions for the other side's limit by having constant off times etc. These methods would be difficult to implement for true bidirectional current mode control as one direction of the current would remain unlimited or uncontrolled. Hence, to attain true bidirectional current mode control, the instantaneous current flowing through the active inductor element should be known at all times (i.e. for both switching cycles) and the inductor ripple current controlled on both sides of the desired set point. This requires that the current through the inductor is measured continuously with as little time delay as possible so as to obtain a true representation of it, and then controlled using both an upper and a lower limit around the desired set point.
This patent sets out a method and circuitry for lossless measurement of inductor current in a converter and using it for hysteretic type true instantaneous bidirectional current mode control. It can be used in many configurations where there is an inductive energy storage element driven by a switching circuit. Typically, this will be a half or full bridge used in a non-isolated buck, boost, buck/boost or inverter configurations.
The first part details a method and circuitry to measure the instantaneous bidirectional current through an inductor in a lossless manner. The second part details a system and circuitry to control the current with true bidirectional hysteretic type control with very good noise immunity. The third part details a method and circuitry to accomplish stability when closing the loop to control the output voltage of a hysteretic current mode controlled converter with a very high gain and accuracy.